Operation of wideband code division multiple access/high speed packet access (WCDMA/HSPA) on multiple 5 MHz frequency blocks (“carriers”) is one further step of evolving WCDMA and HSPA. This mode of operation is often referred to as Multi-Carrier WCDMA or Multi-Carrier HSPA, in the following referred to as “multi-carrier HSPA”.
A multi-carrier arrangement with frequency division duplex (FDD) may be described as a set of downlink (DL) carriers linked to a set of uplink (UL) carriers. The downlink carriers may be adjacent or non-adjacent in the frequency domain, and the same holds for the uplink carriers. More general, carriers do not need to be in the same band and TDD bands could also be used as part of the multi-carrier operation.
The multi-carrier arrangements may also be such that the number of downlink carriers is different from the number of uplink carriers.
The out-of-sync detection is based on fractional dedicated physical channel (F-DPCH), which carries the uplink transmit power control (TPC) commands sent on the downlink. In a multi-carrier HSPA system, the motivation of using multiple fractional dedicated physical channels (F-DPCHs) on different DL carriers is to have reliable out-of-sync detection independently on each carrier since both interference and fading are independent. When there are several downlink carriers then out-of-sync detection based only on the anchor carrier might cause unnecessary radio link failure deteriorating user performance.
WCDMA and HSPA systems make use of mechanisms to control the downlink power, in which TPC commands are sent on the uplink to control downlink dedicated channels (e.g. F-DPCH and other R99 DPCHs) transmit power. When using multiple F-DPCHs on the downlink, there will be an issue of how to convey TPC commands on the uplink for these F-DPCHs. One simple way might be to use multiple UL dedicated physical control channels (DPCCHs) on the uplink. But the cost will be high in terms of power consumption and frequent physical channel setup and release due to that sometime the UE receives data from one carrier with one F-DPCH while sometime the UE receives data from multiple carriers. Another drawback of using multiple DPCCHs, which are mapped on multiple channelization codes in the uplink, is the increase in the uplink peak to average power ratio. This in turn would require UE to further reduce its maximum power in order to meet the radio transmitter requirements such as adjacent channel leakage ratio (ACLR). In simple words the use of multiple DPCCHs would lead to increase in the uplink power back-off resulting in coverage loss.